Several recent meta-analyses of acupuncture for chronic pain have shown that verum acupuncture is not superior to sham/placebo acupuncture. However, these same meta-analyses have also noted significant heterogeneity in acupuncture methods across trials, which complicates combining results. For example, while electro-acupuncture (EA) was superior to sham acupuncture in relieving pain for fibromyalgia (FM), manual acupuncture (MA) was not. In terms of physiologic action, EA and MA are very different procedures. They effect different peripheral targets and induce different psychophysical perceptions, manifest in different brain response. In fact, somatosensory afference may be a key variable in acupuncture analgesia, and the use of some sham needling devices (e.g. Streitberger Needle (SN)) has been criticized since they also produce somatosensation. Moreover, somatosensation may be a particularly important variable for FM, as this chronic pain disorder is known to display altered sensory and nociceptive amplification. Thus, we hypothesize that EA has been more effective for FM because it functions as a desensitization therapy, which when applied repeatedly over multiple treatment sessions, gradually habituates the nervous system to continuing endogenous pain and somatosensory signaling. Our overall goal is to evaluate the impact of acupuncture-induced somatosensory afference on altered neurobiology and analgesia in FM. To test our hypotheses, we will incorporate neuroimaging into a randomized, blinded, longitudinal trial in FM using acupuncture interventions with significantly different amounts of somatosensory afference: (1) EA and (2) mock laser (ML) acupuncture - a relatively new form of sham acupuncture that does not induce any somatosensory afference. Our first Aim will characterize, at baseline, the altered somatosensory-related neurocircuitry underlying chronic pain in FM. Aim 2 will evaluate longitudinal desensitization effects of electro- and mock laser acupuncture on the neurocircuitry underlying chronic pain in FM. Aim 3 will then evaluate the ability of altered neurocircuitry at baseline to predict clinical response to both electro- and mock laser acupuncture. These analyses will provide much needed information about which patients might benefit most from which acupuncture interventions.